Motor driven pump units are typically used in ABS and traction control systems. Cap screws which are acted upon by a defined preloading force in the assembly of the unit are used to attach the cover to the housing body. It has been found that the attachment screws suffer from a more or less great loss in preloading force in the course of time. Because several attachment screws are required, it is unavoidable that there are differences in the preloading force and in the loss in preloading force among individual screws. The result of this state of affairs is an uneven contact force of the cover on the housing body and, consequently, an uneven sealing effect. The disadvantages of the uneven sealing effect occur in a similar fashion when attaching a motor housing to another side of the housing body.
Therefore, an object of the present invention is to provide a unit with structural elements which can be attached to one another with an improved and, more particularly, more even sealing effect. Another objective of the present invention is a simplification and cost reduction of the assembly process.
These objects are achieved by the present invention wherein a motor housing is arranged on another side, and there is provision of at least one attachment means between the motor housing and the cover in such a fashion that the latter components can be attached to the housing body with the same contact force. Because the two structural elements, i.e., motor housing and cover, are urged on the housing body with the same contact force, a homogeneous sealing effect without major differences between the one or the other side may be achieved. In addition, the arrangement of the present invention leads to a reduction in the necessary attachment means because each attachment means fixes both the motor housing and the cover in position.
In a preferred embodiment, no attachment means project from the external edge of the housing body. The result is a closed contour with smooth surfaces where the necessary attachment means are arranged in a space-saving manner.
According to a preferred aspect of the present invention, reduced-shaft bolts are provided as attachment means which suffer from a particularly small loss in preloading force in the course of time.
According to another preferred aspect of the present invention, the cover is made of plastics and has an injection-molded bushing for engagement by the attachment means. These features facilitate the assembly because there is no need for a separate fitting of covers and fastening nuts from different sides. Thus, the bushing and the cover constitute a construction unit which can be handled independently.